644640192 has 168 divisors, whose sum is σ = 2147145312. Its totient is φ = 181094400.

The previous prime is 644640181. The next prime is 644640193. The reversal of 644640192 is 291046446.

644640192 is a `hidden beast` number, since 6 + 4 + 4 + 640 + 1 + 9 + 2 = 666.

It is a tau number, because it is divible by the number of its divisors (168).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644640193) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 244642 + ... + 247262.

Almost surely, 2^644640192 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644640192, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1073572656).

644640192 is an abundant number, since it is smaller than the sum of its proper divisors (1502505120).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644640192 is a wasteful number, since it uses less digits than its factorization.

644640192 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2707 (or 2694 counting only the distinct ones).

The product of its (nonzero) digits is 41472, while the sum is 36.

The square root of 644640192 is about 25389.7654971447. The cubic root of 644640192 is about 863.8515691520.

The spelling of 644640192 in words is "six hundred forty-four million, six hundred forty thousand, one hundred ninety-two".